Method and apparatus for train control



March 3, 1931. N. D. PRESTON 1,794,543

METHOD AND APPARATUS FOR TRAIN CONTROL Filed Feb. 15, 1922 Patented Mar.3, 1831.

ere? mate NEIL PREQEON, OF ROCHESTER, NEW YORK, ASSIGNOR '10 GENERALRAILWAY SIGNAL COMPANY, OF GATES,-NEW YORK, A CORPORATION 'OF NEW YORKMETHOD ANDAPPARATUS FORTRAIN CONTROL Application filed February'15,1922. Serial Ho. 536,750.

This invention relates to automatic train control systems for railways,and more particularly to a method and apparatus for transmitting orcommunicating influences from a trackway to a moving'vehicle or train,dependent upon the presence and location of another train ahead, andadaptable for the control of cab signals, brake control mechanism, orother safety devices.

Briefly and generally stated, the elemental objects of this inventionareto provide a method, and a specific apparatus for practicing suchmethod, by means of which appropriate controlling influences may be com-1 municated to moving trains dependent upon the presence and location ofanother train im-- mediately ahead, which will act inductively throughan intervening air gap without physical contact, will maintain acontinuous communication, so that a change in trafiic'conditions aheadwill be instantly manifested devices'and circuits beingillustrated morewith a View of making the nature. of theinvention readily appreciable,than withthe purpose of illustrating the exact construction.

and arrangement of parts preferably employed in practice. v v V IReferring to the accompanying drawing,

byfinsulated joints 2 into ,tracl: sections'or blocks in the usualway,one block B with the ends of the two adjacent blocks A and 0 beingshown. These blocks are provided with direct current polarized trackcircuits in c n and advantages of the invention will be in the trackrails 1 of the railroad are divided formity. with well-known practice.The

parts and circuits associated with the several blocks are the same, andfor convenience Wlll be given the same reference characters withdistinctive exponent-s. At the entrance end of each block, traffic beingfrom left to right as indicated by the arrow, is a track relay 3 oftheusual neutral-polar type,'wh1ch 1s provided with pole changingcontacts controlling the connection between a track battery 4 and thetrack rails at the exit end of the next pre- The cab signal orcedingblock in the rear. train control system governed by the influencecoimniuncating means constituting this invention may be used with orwithout the usual traclrway ii-iedsignals, and such signals S have beenshown conventionally, without attempting to illustrate their, controlcircuits, which maybe of any one of the well-known types.

it locomotive, cr'other railway vehicle, is

illustrated conventionally as a pair of wheels and anaxle. In accordancewith this invention, t ere are carried by this vehicle, supported,housed, and protected in any suitable manner, .detectingcoils 55 whichare carried in front of the first pair oi wheels and axle of thevehicle, directly over the track rails 1. These coils 5 may be of anysuitable shape, and are mountedon a suitable frame supported byanti-friction bearings,

so as to be rotatable on an axis extending along the rails. In otherwords, these coils are arranged so that, when rotated, they will cut themagnetic lines of force or flux which i encircle or surround the trackwhile the direct current from the track battery 4: is flowing therein.vThe detecting coils 55 are provided with commutators and brushes, designated 6 630i suit-able construction,- corresponding to that commonlyemployed in direct current generators, to convert the alter natin'g E.M. F. generated in said coils into a uni-directional voltage. Thesereceiving coils 5.5 are continuously rotated by some suitableinstrumentality. In the specific arrangement shown, small direct currentmotors of the shunt type 7'?, connected in multiple, and suppliedwithcurrent from a suitable battery 8 or other source, are directly coupledsi nifies clear or proceed, the lumpy (yellow) s1 to the frames orsupports for the coils 55 While under favorable conditions the generatedcurrent obtainable in the receiving coils 55 may be employed to actuatean electro-responsive device directly, on-account of practicallimitations, it is preferred to amplify the voltage manifestations insaid coils, so as to obtain an amount and form oi ener 'y adaptable forthe operation of ordinary relays of the tractive type orequivalcnttypes. For thispurpose a thermionic amplifier or relay of the well-knownvacuum tube type is preferably employed, although any suitableelectro-responsive device with amplifying characteristics may beemployed. The thermionic amplifiershown, commonly termed an audion,comprises a filament F, a grid G, and a plate P. Since thecharacteristics and mode of operation of these audions are wellunderstood in the art, it is -deemed suliicient to point out the way inwhich such characteristics are utilized in connection with thisparticular invention.

Referring to the specific arrangement shown, two audions 9 and it) areused. The filament F or" each audion is heated by a battery'll in theusual way. In the plate circuit of'the audion 9, energized by battery12,,is connected a relayE which may be of the tractive, d mamometer, orother type, best adapted for the particular worlring conditions underwhich the invention is practiced.

,Itis contemplated that the contacts or circuit controlling elements or"this relay will be biased or counterweighted so as to change as theenergizing current of the relay is cut oil, or decreased below the holdup value. Tnthe plate circuit of the audion l0, energized by a battery13, is a similar relay The contacts for the relays R and R are shownconventionally; and while the selective operation of these contacts maybe employed to control cab signals or any suitable form or" traincontrol mechanism, or both in a simplified ar rangement as illustrated,three lamps, 7', y and g and a device K, are governed in con formitywith the energization control of said relays R and R The lamp g may begreen orany other suitable color, and when lighted signifies caution,and the lamp 1 (red fies stop or danger.

The device K may talre various forms, and since its specificconstruction or mode of operation forms no part of the presentinvention, it is unnecessary to discuss its operating characteristics indetail, it being noted that, according to the specific arrangement ofcircuits shown, this device K is one which is maintained inactive whileenergized, and is set into operation or rendered active when The deviceK, when set into Clo-energized. operation, may cause an immediatebralreapplication in any suitable manner, or bralre application in case theengineer fails totalre appropriate action, or a brake applicationdependent upon the vehioles speed being in eXcess of some fixed speedlimit, or in excess of a speed limit changeable in accordance with theprogress of the vehicle. It may be added that, on account ofthecontinuous control characteristics of the influence communieating meansconstituting this invention, a cyclic train speed control of the typeshown and. described, for example, in thepatent to Simmen, 1,150,309,August 17, 1915, may be employed to advantage,

The control circuits for the lamps 1", 3 and g, and the device K, may bereadily tracedon the drawing. VVith the relay R up and the relay R down,the lamp 9 is lighted and the device K energized, corresponding to cleartraffic conditions. Nith the relay R down and the relay R up, the lamp yis lighted, and

the device K deenergized, corresponding to caution conditions. With boththe relays R and R down, the lamp 1' is lighted, correspending to dangeror stop conditions, the device K being still deenergized.

The receiving coils 5-5 are connected in series, through theircommutators 6-45, and are connected in the grid circuits of the twoaudions 9 andll) ina reverse manner. The circuit connecting thereceiving coils 5 and 5 in series and maintaining a potential on thegrid G of the audion 9 with respect to its filament F may be traced asfollows :-commencing at the grid G, wires 1% and 15, upper brush ofcommutator 6 through the coil 5?;

lower brush of said commutator, wire 16, upper brush of commutator tl,through coil 5, lower brush, of said commutator and wires 17 and 18 tothe filament F. The coils 55 are so wound, and connected that thevoltage induced therein, when current flows in opposite directions inthe respective track rails, will be cumulative or additive. Toillustrate, assuming a certain direction of current flow in the trackrails 1 and a certain direction of rotation of the coils 5 and 5 thesecoils are so wound and connected to the commutators 6 andli thattheupper brush, for example, of the commutator 6 will be positive, asindicated, whereas the lower brush of the commutator 6 willbe negative;WVithout tracing the circuits,iit can be easily seen from the drawingthatthe upper brush of the comnutator 6 assumed for the purposes of eX-planation tojbe positive under clear traliic conditions illustrated inthe drawing, is conected' to the grid G of he audion 9, while thefilament l? of this same audion is connected to the lower brush of thecommutator 6, thereby making the potential of this grid positive withrespect to the filament. Similarly. the lower or negative brush of thecommutator 6 is connected to the grid G of the FAD tivewith respect toits filament. Onaccount of thereverse connections of the grids of theaudions 9 and 10, with any given direction of current in the trackrails, the potential onzthe grid G of one audion is positive, for example, and that on the other audion negative. The various circuits,voltages, and characteristics of the audions 9 and 10 are selected orproportioned such thatIa positive potential on the grid of eitheraudion-S) or 10, will allow sufiicient current to flowin the platecircuit ofthat audion to pick up and hold up thecorresponding relay vRor R whereas with a substantially zero potential on said grid, the

plate current is so reduced as to allow the corresponding relay todrop'away inresponse to its biasing force. On account of the wellknowncharacteristics of the vacuum tube amplifier or audion, when the gridpotential is reversed and becomes negative with respect to its filament,the current is less'than when the grid, is at a zero potential and muchless than when at a positive,potential.

From consideration of the polarized track circuits illustrated, itwillbe evident that, ,under clear traiiic conditions,'the current in thetrack rails of each blockwill flow in one direction in one rail,.and inthe opposite direction in the other rail, as indicated, for example, bythe arrows a.- When there is a train in the block, as the bloclrC, thetrack relay 3 of that block is caused to drop its armature inthe usualWay, and this reverses the connections of the track battery to the trackrails of the block next in the rear, as the block B, so that thecurrents in track rails of this block in the rear, while still flowingin opposite directions relatively to each other, are in the oppositedirection to that under clear traffic conditions. lVith a train in ablock, its wheels and axles form a shunt of very low resistance, so thatvery little, if any,

current will flow through the track rails in front of a vehicle enteringtliat'sameblock,

Thus, under clear traiiic-conditions, th-e'voltage induced in the coils55 is of one.

polarity, causing one relay R to pick up and the other relay R to drop;undercaution traflic conditions,,the polarity ofthe voltage generated inthe coils 5- 5 is reversed, re? versing the potentials on grids of theaudio'ns 9 and 10 and causing the relay to drop and the relay R to pickup; and under dangerous trafiic conditions practically no vol age isgenerated in the coils 55 reducing the potential on vthe grids of theaudions 9 and 10 to zero, and causing both relaysR and R to drop. Inthis way, there are received on the car the three indications of clear,caution, and stop; and these indications maybe used in any suitablemanner, as indicated above, to control the brakes of the vehicle andregulateits movement arbitrarily,

or dependent upon speed or other condition:

These three indications of clear, caution, and

tions, a change to a more favorable indica- 1 tion taking placeautomatically and instantly as soon astraiiic conditions ahead cleanup.Itis noted that one audion and relay are sufficient for two indications,and since certain types of speed governed brake control mechanism,require only two indications for their proper control, it isevident thatan adequate train control system may be devised in accordance with. theprinciples of this invention with the use of one relay and one audionalone; I

Itwill beiobse rved thatthis invention provides the reception of thedesired controlling influences without the addition of anytrack o,devices or source of energy. The influenceis communicated continuously,and the various circuit connections are such that interruption thereof,depreciation or failure of the car carried batteries, crossings betweenwires, and other defects likely to occur, will all cause cessationJotthe communicating influence and produce an effect on the sideofsatety. .Also, such continuous control possesses the desirable characteristicof instantly manitesting on a following car at any point in ablockachange intraliic conditions in the next 1 block in advance. F orexample,if thetrain is in theblock B, anddanger conditionsin theblock Care indicated by the vdropping of'the track relay 8?,apparatus on thefollowing train will instantly respond as soon as the conditions inblockC change from danger to caution or clear, entirely irrespective ofthe position of said following train in the block :13. This lattercharacteristic is obviously of great value in speedIcontrolsystems inwhich a vrestrictionupon tra n movement is imposed and continued untilanautomatic release or restoration is obtained from the trackway; and, theindications of the cab signalidevices, f used, correspond correctly tothe 1nd1cations of the traclrway fixed signals.

It will be appreciated that the relatives i zes and proportions of theparts and electrical constants of the various clrcuits aresusceptible'of considerable adaptation in practice, in

order to obtain the most favorable results 'undera given set of workingconditions; and consequently, no attempt has been made to,

show and describe any specific arrangement.

It should be understood, however, that two in track rails, it beingevident that stray currents flowing in opposite directions in the re- 7spective track rails, and of a suiiicient magninot be improperlyaffected by any stray tude to cause false operation of the train controlequipment, will likewise have a tendency to produce false operation ofthe'regular track relay. Putting it another way, it may be said that thetrain control apparatus will currents in the track rails which would notalso tend to produce improper track circuit operation, a condition whichwould have to be in some way remedied.

Since, the length, ballasted conditions, battery voltages, and the like,for different direct current track circuits now in common use on Vrailroads are somewhat variable, it may be necessary in practicing thisinvention to modify these factors in some cases in order to obtainsatisfactory operation of the train control system. .For example,so-called cut-sectial at the relay end; and similar adaptations made inexisting track circuits in a manner ev1dentto those sk1lled in the art,so as to obtain the desired value of current in the track rails in frontof a train on a given track circuit at the difierent points in thetravel of such train. With proper provision for amplification, however,the current in the track rails may be very small; and except for thedanger of possible interference by feeble magnetic fields near the trackrails from other sources than the proper current,-no arbitrary amount ofcurrent in the track rails isnecessary to prac ice the invention. Thedetecting or receiving coils 55 are preferably used Without iron coresso as to avoidpos'sible'difiiculty with the effects of residualmagnetism, and similarly the instrumentality driving these coils, whichhas been shown for simplici ty as small direct currentmotors, will likewise be designed or protected in the practical application of theinventionto avoid such interference.

It is pointedout in this connection that a magnetic field through bothof the. coils 5-5? in the same direction produces no efiect, since thevoltages generated in these coils in such a case will oppose each other.In short, while appropriate design and selection of electrical constantsare necessary in practicing thein vent-ion under varying workingconditions existing in practice, as a general proposition, the system ofcommunicating influences in the manner characteristic of this inventionis adaptable to direct current track circuits as now commonly used,thereby enabling the application of the train control system torailroads without material change in their trackway equipment, providingadditional sources of current, or adding to the trackway anythingthatmay interfere with their rolling stock clearances.

The specific construction and arrangement of parts and circuits'shownand described are obviously susceptible of much adaptation andmodification without altering the nature and characteristic of theinvention; and I desire to have it understood that this drawing andspecification are merely an illustrative disclosure of oneparticular'type of means for pracicing the method and carrying out thefunctions'of the apparatus constituting my invention;

What I claim is p 1; The method of communicating influences to movingtrains "in conformity with trafficv conditions, which consists insupplying to the traclr'rails a direct current of one or the otherpolarity, converting the field of flux around the track rails createdthereby into a current of like polarity on a moving canand amplifyingsuch current on the car and utilizing ity to govern safety mechanism inconfornity with the existing polarity of current in the track rails. Y

2. The method of communicating influences to moving trains for traincontrol purposes, which consists in supplying to the track railsnormally a direct current of one polarity, reversing the polarity ofsuch current for a limited distance in the rear of a train, detectingsuch current without physical contact, and governing safety mechanism ona following trainin accordance with such change of polarity.

3. The method of communicating influences to moving trains for traincontrol purposes, which consists in continuously supplying acontrolcurrent to a moving car by the presence of a continuous direct currentin a conductor disposed along the path of movement of said our,amplifying such current and utilizing it for governing cab signals ortrain control mechanism.

a. The method of communicating influences to moving trains for traincontrol pur poses, which consists in supplying a control currentcontinuously to a moving car without physical contact by a continuousdirect current in a conductor disposed alcng the path of movement of thecar, modifying the direct current in the conductor at times tocorrespond with the varying traffic conditions, and'utilizing variationsin the current on the car for cab signals or-train control purposes;

n or .5. The method of communicating influences ton'ioving trains fortrain control purposes, which consists in changing the existence and thedirection of how of direct current in a conductor disposed alongthe'p'ath of movemen t of a vehicle, producing'without physical contactwith said conductor a current in a circuit wholly on the car whichdepends upon and varies with the presence and also polarity of saiddirect current in said conductor, and utilizing such flow of current insaid car carried ci"cuit for train control purposes. a V 1 6. A methodof providing the control influences suitable for cab signals or traincontrol purposes, which consists in dividing the track rails intoinsulated track sections, supplying direct current to the rails of eachtrack section the polarity of WhlCll'lS dependent upon the presence orabsence of a train in the next track section in advance, and producingin a circuitwholly ona following car a current corresponding to anddependent upon the presence of such current in the track rails, andutilizing the currentin the car carried circuit for train controlpurposes.

7. A method of providingthe control influences suitable for cab signalsor train con trol purposes, which consists in dividing the track railsinto insulated track sections, supplying direct current to therailsof'each track section of a polarity dependent upon the presence orabsence of another train in the next track section in advance,converting the field of flux around the track rails into a current on afollowing vehicle, amplifying said current on the following vehicle, andutilizing the amplified current to govern cab signals or train controldevices.

8. The method of communicating train movement influences trom'thetrackway to moving vehicles for cab signals or train control purposes,which consists in forming a series of normally closed circuits, partlyon the track and partly on the moving car with an interposed air'g'ap,and supplying said circuits with direct current and providing thereindevices for detecting and amplifying a constant field of magnetic flux.V

9.- In a system of cab signals or train control'tor railroads, thecombination withpolarized direct current track circuits, of means on thecar for producing without physical contact with the track rails aderived voltage at all times corresponding to the existence and polarityof the current in said track circuits.

10. In a system of cab signals or train control for railroads, thecombination with a track divided into track sections each havinga-polarize'd direct current track: circuit, ot

automatic means on the car for detecting and amplifying the eltect ofthe current ot said track circuits flowing 1n the track rails.

11. In a system of cab slgnals or train control for railroads, thecombination with a conductor along the track inwhich continuousdirectcurrent is'flowing,means 0n the moving car detecting the field offiux'created by such current, a device to be governed, and

amplifying means controlled by the detecting ii cal contact.

13. In a system of cab signals or train control tor railroads, thecombination with a track rail carrying continuous direct current or" onepolarity, of car-carried means for detecting. the flow of said currentwithout physical contact, a device to be governed, and amplifying meansresponsive to the detecting means for governing said device.

14;. in a system of cab signals or train control .tor railroads,thecombination with a track rail carrying direct current, car-carriedmeans comprising detecting and ampli tying devices responsive to thepresence and polarity of said current. I p

15. In a system of cab signals or train c011- trol tor railroads, thecombination with a' track rail and a source of direct current, trackcircuit control means controlling the connections between said sourceand the track rail, and means for amplifying and detecting the flow ofcurrent in said rail without trollable device on a car tending to assumeits act ve condition, and means responsive to the presence and polarityof the current in the track rails without physical. contact forgoverning said device said'means convertin' 'b electro-ma neticinduction the m agnetic field of said current in the track rails into anelectrical difference of potent ial. a a

17. A train control system comprising, a pair of track rails and asource of direct current connected thereto, and voltage producingmeansion a car disposed in front of first pair of wheels and axles, andresponsive to the flow of said current in said track rails. 18. Car,apparatus for train control sys tems comprising, a constantly rotatingcoil carried relatively close to and above the track rail on which thecar runs to cutthe magnetic flux produced by current How in said rail.

19. Automatic means for detecting the presence of direct current in thetrack rails on which vehicles travel comprising, means carried by thecar in front of its first air of wheels and axle for producing a dierence or potential corresponding to the magnetic field around saidtrack rails which is pro duced by the flow of direct current therein,

and biased electro-responsive means and a car-carried source of currentcontrolled by said diiierence of potential.

20. Influence communicat ng means of the character described comprising,in combination with a conductor on the trackway carrying current,ofcar-carried apparatus comprising, coil'in the field produced by thecurrent flow in said conductor, means for ro-- tatingsaid coil, acommutator, a relay, and amplifying means connecting said coil andrelay.

r 21. In a train control system, the combination with a conductordisposed along the path of travel of the vehicle a d carrying directcurrent, and means on a vehicl for detecting without physical contactthe existence of such current in the track rails comprising, a

generating coil, an amplifying means and an electrO-responsive device.

'22. In a train control system. the combination with the rails of tracksections in which direct current flows in opposite directions underclear and caution trafiic conditions, means on a car for changing thefield of flux of such current into a potential, safety mechanism on thecar, and amplifying means responsive to said potential for governingsaid safety mechanism.

23. A system of continuous inductive control for railway vehicles'co iprising, in combination with polarized direct current track circuits,detecting and amplifying means on combination With detecting andamplifying means on a car responsive to constant unidirectional magneticfield, of track circuit control m ans for supplying such field to thecar-carried means at all points in the travel ot the carf p v 25. Asystem of inductive continuous control for cab signal and train controlsystems characterized by the detection and amplification of the effectof continuous direct current in a conductor along tle path of movementof the vehicle without physical contact.

26. In a cab signalor train control system for railroads, in combinationwith a sectionalized railroad track, a battery for each section, meansacting when a given section is not occupied to connect the battery ofthe section next in the rear across the track rails at the exit endthereof, means carried on the car relatively close to and over eachtrack rail in front ofthe first pair of wheels and axles of the cartorproducing a uni-directionalvoltage of a definite polarity which isderived from the current flowin said tracl: rails, and means on the carincluding a car-carried source or" energy and governed by said voltage.

27. In a train control system, a track divided into sections, trafiiccontrolled means automatically applying a uni-directional difterenceofpotential across the track rails of each section at its exit end toproduce a direct current, car-carried electroresponsive means and asource of energy on the car connected thereto, and means carried bythecar over a track rail and acting automatically to change the flow ofcurrent from said source to the electro-responsive means incorrespondence with the direction or" said direct current in the trackrails without circuit interruptions' i V 28. In a train control system,the combination with a line of track rails in which direct current flowsin opposite directions, and means carried on the car in front of theoperati or a with the magnetic field produced by the flow of saidcurrent in the track rails for producing inductively a difi erence ofpotential on the car having a predetermined polarity corresponding tothe direction of flow of said current in said track rails.

29. In an automatic traincontrol system for railroads having tracksections divided into blocks each having a track battery con nectedacross the track rails at one end, car apparatus comprising a relay, asource of current for energizing said relay, a vacuum tube amplifierhaving its plate circuit connected to said relay, and means disposed ininductive relation to said track rails in front of the first pair ofwheels and axle of the car and responsive to the constantuni-directional magnetic field produced by the current flow in saidtract: rails from said buttery for imposing a corresponding potential onthe grid of said amplifier.

30. In a system of cab signals or train control for railroads, thecombination with an insulated track section, a source of direct current,and automatic means for connecting said source across the track rails atone end of said section thereby producing a flow of constantuni-directional current in the track rails; of car-carried means forproduci' 31. In a system of the character described,v

the combination wi -h the track rails of a track section in whichcurrent of a predetermined polarity flows in opposite directions, of acar-carried element rotating in the magnetic field of the current insaid track rails and generating a voltage of cor-' responding polarity.

v32. In a system of the character described, an insulated track section,a source of current connected across the track rails of said section atone end thereof, and car-carried conductors maintained in constantmotion on the car in the magnetic field produced around the track railsby the flow of said current therein, said conductors generating avoltage derived solely from such current flow. I

- 83. In a cab signal or train control system for railroads havingtracks divided into track sections, each section having continuousdirect current flowing in opposite directions in its track rails undercertain traiiic conditions, car-carried means having an inherenttendency to assume its active controlling condition and automaticallymaintained inactive by the 'efiect of voltage in a carcarried circuitderived from the flow of said direct current in the track rails withoutphysical contact with said track rails.

.34. In a system of the character described, the combination with atrack section having direct current flowing in opposite directions inits track rails, car-carried apparatus comprising a plurality ofcircuits to be controlled,

electro-resp onsive means having a tendency to open all of said circuitsand operable by unidirectional voltages of different polarities. tomaintain certain of said circuits closed in conformity with the polarityof said voltages, and means for producing on the car without electricalconnection to the track rails unidirectional voltages which are derivedfrom the flow of said direct current in the track rails and have relatedpolarity.

35. In a train control system, the combination with a track sectionhaving current fiowing in opposite directions in its track rails undercertain traffic conditions, car-carried apparatus comprising a relay, anaudion controlling said relay, and means for appl ing to the inputcircuit of said audion a unidirectional voltagc derived solely from themagnetic field of said current flow in the track rails.

36. In a train control system for railroads having track sections inwhich direct current of different polarities flows in opposite direc--tions in the track rails, car-carried apparatus comprising twothree-element vacuum tube amplifiers, and means varying the gridpotentials of said amplifiers in the opposite sense to correspond withthe polarity of the direct current flowing in the track rails.

37. In a system of the character described, the combination with a trackrail in which current flows, of a coil, and a commutator on a carconstantly rotated in the field produced by such current flow.

38. Car apparatus for train control systems comprising, a coil in frontof the first pair of wheels and axle of the car and'disposed over Wayvehicle at all points in its travel any one of a plurality of controlinfluences suitable for cab signals or train control purposes, whichconsists in applying a uni-directional electro-motive-force across thetrack rails at the exit end of an isolated track section so as to causea flow of direct current in opposite directions in said track rails,varying the polarity of said electro-motive-force for each track sectionin correspondence with the presence or absence of other trains ahead,and producing on a vehicle at all points in its travel in each traclrsection and without electrical contact with the track rails a voltagecorresponding to and derived from the flow of said direct current in thetrack rails of that section.

40. Ina train control system, the combination of a railway track, avehicle thereon, said track divided into blocks, means controlled bytrafiic conditions for energizing a rail of said blocks with continuousdirect current,

means on said vehicle responsive to, the current in said rail andamplifying the effect thereof.

41; In a train control system, the combination of a railway track, aVehicle thereon, means for energizing a rail of said track with directcurrent, a device on said vehicle responsive, to the current in saidrail and controlling a circuit, means for amplifying the current in saidcircuit and means for controlcurrent delivered by said coil.

48; In combination, a railway train, generating means located on saidtrain and comprising a rotating armature, means located in the trackway.for continuously supplying magnetic flux tosaid generating means whentraflic conditions are safe but not when traffic conditions aredangerous, means located on the train for driving said armature, and

train governing means controlled by current suppliedhysaid generatingmeans.

44. In combination, a railway train, gen eratingmeans on said trainhaving an armature, means located in the trackway for supplying saidgenerating means with magnetic ling the polarity of the current in saidcirflux of one relative polarity'o"; the other in accordance withtrafiic condiaions, means on the train for driving said armature, andtrain governing apparatus responsive to the polarity of theelec'iro-motive force supplied by said generating means.

In testimony whereof 1 hereto my signature.

NEIL DPRESTON.

